Hubble Space Telescopeand United Kingdom Infrared Telescope Observations of the Center of the Trifid Nebula: Evidence for the Photoevaporation of a Proplyd and a Protostellar Condensation

The Trifid nebula (M20) is a well-known prominent optical HII regiontrisected by bands of obscuring dust lanes and excited by an O7.5 star HD164492A. Previous near-IR, mid-IR and radio continuum observations of thecluster of stars at the center of the Trifid nebula indicated circumstellardisks associated with hot stars with envelopes that are photoionized externallyby the UV radiation from the hot central star, HD 164492A. Using WFPC2 of theHST, we present evidence of a resolved proplyd in H$\alpha$ and [SII] lineemission from a stellar source emitting cool dust emission. Using UKIRT, aninfrared observation of the stellar source with a proplyd indicates a late F --mid G spectral type. We also note a remarkable complex of filamentary andsheet-like structures which appear to arise from the edge of a protostellarcondensation. These observations are consistent with a picture in which thebright massive star HD 164492A is responsible for the photoevaporation ofprotoplanetary disks of other less-massive members of the cluster as well asthe closest protostellar condensation facing the central cluster. Using theevidence for a proplyd, we argue that the massive and intermediate mass membersof the cluster, HD 164492C (B6 star) and HD 164492 (Herbig Be star) have disksassociated with them.Comment: 13 pages, 5 figures, AJ, in pres